Choroideremia is a rare X-linked progressive degeneration of the choroid, retinal pigment epithelium and photoreceptors of the eye. The typical natural history in afflicted males is onset of nightblindness during teenage years, and then progressive loss of peripheral vision during the 20's and 30's leading to complete blindness in the 40's. Female carriers have mild symptoms most notably nightblindness but may occasionally have a more severe phenotype.
The disease is caused by mutations in the REP1 gene, (Rab escort protein 1), which is located on the X chromosome 21q region. In most cells in the body, the REP2 protein, which is 75% homologous to REP1, compensates for the REP1 deficiency. In the eye, however, for reasons that are not yet clear, REP2 is unable to compensate for the REP1 deficiency. Hence in the eye, REP polypeptide activity is insufficient to maintain normal prenylation of the target proteins (Rab GTPases) leading to cellular dysfunction and ultimate death, primarily affecting the outer retina and choroid.
There is no treatment for choroideremia, and there is a lack of models to assess therapeutic strategies. There is a need for provision of such a therapy.